POS0660 FACET JOINT INFLAMMATION IS RARE, BUT WHEN PRESENT IT IS ASSOCIATED WITH FACET JOINT ANKYLOSIS IN RADIOGRAPHIC AXIAL SPONDYLOARTHRITIS PATIENTS FROM THE SIAS COHORT
Authors: M. De Hooge, R. Stal, A. Sepriano, X. Baraliakos, M. Reijnierse, J. Braun, D. Van der Heijde, F. A. Van Gaalen, S. Ramiro
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> There is still little known on posterior element (PE) inflammation and ankylosis in the facet joints (FJ) of patients with axial spondyloarthritis (axSpA). <h3>Objectives</h3> To assess whether PE inflammation, in particular in the FJ, is associated with new FJ ankylosis on MRI one year later, in patients with radiographic axSpA (r-axSpA). <h3>Methods</h3> Patients with a diagnosis of r-axSpA recruited from Germany (Herne) and the Netherlands (Leiden) were included in the Sensitive Imaging in Ankylosing Spondylitis (SIAS) observational cohort when ≥1 inflammatory lesion on MRI of the spine and 1-18 syndesmophytes were present. Spinal MRIs were performed at baseline, 1 and 2 years. PE inflammatory lesions and FJ ankylosis were both assessed on MRI, per vertebral unit (VU) level by 3 readers independently. FJ inflammation in the cervical spine was not assessed. The probability of developing FJ ankylosis after one year was described conditional on the presence or absence of PE/FJ inflammation at baseline. Multilevel time-lagged auto-regressive GEE was used for the association between PE (or FJ) inflammation and the development of FJ ankylosis one year later, taking the reader and VU levels into account. <h3>Results</h3> In 58 patients MRI scores of at least 2 readers were available. Patients' average age was 49±10) years and 85% was male. Inflammation in PE or FJ at baseline was seen in 34 (59%) and 14 (24%) patients respectively. PE inflammation was distributed throughout the whole spine but most prevalent in the lower part of the thoracic spine (9%-16%). FJ inflammation was infrequently present and was more often reported in the upper thoracic spine (2%-5%) (Figure 1). FJ ankylosis was reported in 15 patients (26%) at baseline and 17 patients (29%) with follow up visits. FJ ankylosis was mainly present in the upper half of the spine (Figure 1). In 19 patients (33%) the development of new FJ ankylosis over 1 or 2 years was seen by at least 1 reader. Of the VU levels with PE or FJ inflammation only very few showed new FJ ankylosis after one year: 2 and 1 VU levels, respectively (Table 1). There was no association between PE inflammation and the development of new FJ ankylosis in the same level after one year (OR=1.15, 95%CI 0.55-2.42). However, FJ inflammation was associated with new facet joint ankylosis one year later (OR=3.79, 95%CI 1.47-9.75). <h3>Conclusion</h3> PE inflammation and FJ ankylosis on MRI were infrequently observed in patients with r-axSpA. No association was found between inflammation in the PE and the development of FJ ankylosis. However, when inflammation in the FJ is present the likelihood of developing FJ ankylosis after 1 year is over 3 times higher compared to FJ without inflammation. This finding adds to the pathophysiological relationship between inflammation and ankylosis at the same anatomical location of the axial skeleton in patients with axSpA. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Manouk de Hooge Consultant of: UCB, Rosalinde Stal: None declared, Alexandre Sepriano Consultant of: Abbvie, UCB and Lilly, Xenofon Baraliakos Consultant of: AbbVie, BMS, Celltrion, Eli Lilly, Galapagos, MSD, Novartis, Pfizer, UCB, Grant/research support from: AbbVie, MSD, Novartis, UCB, Monique Reijnierse: None declared, Juergen Braun: None declared, Désirée van der Heijde Consultant of: AbbVie, Bayer, BMS, Cyxone, Eisai, Galapagos, Gilead, Glaxo-Smith-Kline, Janssen, Lilly, Novartis, Pfizer, UCB Pharma, Floris A. van Gaalen Consultant of: Novartis, MSD, Abb Vie, Bristol Myers Squibb, Grant/research support from: Stichting vrienden van Sole Mio, Stichting ASAS, acobus Stichting, Novartis, UCB, Sofia Ramiro Consultant of: AbbVie, Eli Lilly, MSD, Novartis, Pfizer, UCB, Sanofi, Grant/research support from: AbbVie, Galapagos, MSD, Novartis, Pfizer, UCB.